The implementation of Water Alternating (WAG) injection to obtain optimum recovery in Cornea Field, Australia

摘要

The Water Alternating Gas (WAG) process is a cyclic process of injecting alternating water followed by gas. The main purpose of WAG injection is to improve both macroscopic and microscopic sweep efficiency, maintaining nearly initial high pressure, slow down the gas breakthrough and reduced oil viscosity. WAG injection also decreases the residual oil saturation resulted from the flow of three phases and effects associated with relative permeability hysteresis. The study area is in the Cornea Field located in Browse Basin, Western Australia. This study is conducted because there is no investigation on WAG injection feasibility in this field. In this study, two-phase bounding imbibition and drainage relative permeability model (Stone 1 and Stone 2) along with two-phase hysteresis model (Land, Carlson or Killough) were used. From the result, Carlson two-phase hysteresis model with Stone 1 correlation shows more oil was recovered. Therefore, it is a feasible model to be used compared with other models. From sensitivity analysis, it shows that highest oil was recovered at WAG ratio 1:1. Since it is a miscible reservoir, 1:1 ratio is more efficient and it is insensitive to trapping. Also, oil production increased with the shortest WAG cycle time at 180 days due to minimum miscibility pressure reached. In addition, it is best to inject water as the first phase to be injected into the reservoir compared to CO2 because water has high mobility ratio while CO2 can result in early breakthrough in the reservoir.